A population has certain attributes which an individual organism does not have. An individual may have birth and death, but a population has birth rates and death rates. An individual is either a male or a female but a population has a sex ratio (e.g., 60 per cent of the population are females and 40 per cent males). A population at any given time is composed of individuals of different ages. Age distribution is the proportionate numbers of individuals in successive age groups in a given population.